Leonardo da Vinci designed an early hygrometer to measure changes in air moisture.
A hygrometer is an instrument for measuring humidity, especially relative humidity. Leonardo’s version used a material that gained weight when it absorbed moisture from the air. The change could then be compared with a dry reference material, providing an indication of atmospheric dampness.
Leonardo’s hygrometer belongs to his broader investigations of weather, water, air, and natural processes. It was not a modern electronic sensor and did not provide readings in the precise percentage format common today. Instead, it used a physical change caused by moisture as the basis for measurement.
The instrument is sometimes confused with a barometer, which measures air pressure, or an anemometer, which measures wind speed. Leonardo also studied wind and atmospheric effects, but humidity measurement is the specific purpose of a hygrometer.